Global navigation satellite systems (GNSS) such as the Global Positioning System (GPS) provide autonomous geo-spatial positioning with global coverage. GNSS satellites broadcast signals from space that receivers use to estimate their three-dimensional location (latitude, longitude, and altitude).
Currently, two main types of positioning are used by GNSS: absolute positioning and relative positioning. Absolute positioning attempts to find a user's position relative to an absolute (i.e., latitude, longitude) coordinate system. Relative positioning attempts to find the position of a first user (a “rover”) relative to a second user (a “reference”). In the latter case, both users may be stationary, both users may be moving, or one user may be stationary and one user may be moving.
Typically, a GNSS receiver makes two measurements in order to perform relative positioning: a code measurement and a carrier phase measurement. These measurements are used to estimate the distance from the user to the satellite transmitter. However, ambiguity in the carrier phase measurement may jeopardize the accuracy of this process. Dual-frequency (L1/L2) GNSS receivers are typically able to compensate for the ambiguity because they make a second set of linearly independent code and carrier phase measurements. However, less expensive single-frequency (L1) GNSS receivers are not able to take advantage of such additional measurements.